Vertex buffers support

[kvark]

Closes #101
Example bits from the updated bunnymark:

#[derive(blade_macros::Vertex)]
struct SpriteVertex {
    pos: [f32; 2],
}

            vertex_fetches: &[gpu::VertexFetchState {
                layout: &<SpriteVertex as gpu::Vertex>::layout(),
                instanced: false,
            }],

rc.bind_vertex(0, sprite.vertex_buf);

TODO:

• API update
  • more vertex formats
• derive macro
• bunnymark example update
• Implementation
  • Vulkan
  • Metal
  • GLES
  • WebGL
• prototype in Zed

This is pretty much done, and it opens the doors properly to use GLES backend with real geometry. However, I realized that porting Zed to vertex buffers isn't going to be as straightforward as I thought. Both Rust and WGSL side structures are deeply nested in it, and that's not expected by either Naga or Blade today. We may need to have additional changes here once we confirm with Zed.